1. Field of the Invention
The present invention relates to a screw for a double-shaft extruding device and a double-shaft extruding device. In particular, it relates to a screw for a double-shaft extruding device and a double-shaft extruding device for extruding a material to be extruded, such as rubber or plastic, into a sheet form.
2. Description of the Related Art
An example of a double-shaft extruding device for extruding a material to be extruded, such as rubber or plastic, into a sheet form is disclosed in Japanese Patent Application Laid-Open No. 2-36920.
As illustrated in FIG. 6, in a double-shaft extruding device 70, screws 74 are supported horizontally and rotatably by a casing 72. A hopper 76 having a top opening is provided at the side of the casing 72 at the base portions of the screws.
A discharge opening 78, which is open in the axial direction of the screws, and a roller die 80, which is adjacent to the discharge opening 78, are provided at the side of the casing 72 at the distal ends of the screws. The portion of the screw 74 which opposes the hopper is a feed portion 74A, and the distal end portion of the screw 74 is a compression portion 74B.
Accordingly, a material to be extruded which is supplied from the hopper 76 is extruded from the discharge opening 78 by the rotating screw 74 via the feed portion 74A and the compression portion 74B. The material to be extruded is made into a sheet form by the roller die 80.
However, in the double-shaft extruding device 70, the cross-sectional area S of extrusion formed by a shaft 82 of the screw 74 and a flight 84 provided on the outer perimeter of the shaft 82 is, from a shaft distal end 82A to a shaft proximal end 84B, similar to graph A in FIG. 5. A region W, where the cross-sectional area S of extrusion hardly varies, exists at an area of a rotational angle of 300.degree. to 540.degree. from the shaft distal end along the flight 84. As a result, the discharge of the material to be extruded, such as rubber, is not smooth in the region W. Further, the material cannot be completely extruded, and some may remain in the interior of the device. Work is required to remove the remaining material, and productivity deteriorates. There is room for improvement with respect to the remaining and removal of the material to be extruded at the distal end portion of the shaft.
Conventionally, the distal end portion of the screw of an extruding device for extruding a material to be extruded, such as rubber or plastic, into a sheet form has generally been cone-shaped or bowl-shaped. The surface of the distal end portion of the screw is generally chrome plated. As a result, there are no convex and concave portions on the surface, that is the surface is smooth.
However, during the extruding operation, the screw itself is heated. Further, during the extruding process, the temperature of the screw rises due to friction between the screw and the material to be extruded. The temperature of the material to be extruded also rises, and the stickiness thereof increases. The material to be extruded therefore adheres to the surface of the distal end portion of the screw.
Because the roller die is located ahead of the screw, high pressure is applied to the screw distal end portion of the shaft distal end portion, and the material to be extruded remains thereat. The material to be extruded adhering to or remaining at the distal end portion of the screw presents a drawback.
Further, the extrusion work is effected in a single apparatus, and various materials to be extruded are extruded therein. Therefore, after the extrusion of one material has been completed, the next material is then extruded. If the previous material sticks to the distal end of the screw of the shaft distal end, the material becomes mixed with a different material, which presents a drawback with respect to the quality of the material.
As a result, in order to prevent the above-described drawback, each time a different material is extruded it is necessary to visually determine whether the previous material has adhered. If some material has adhered, manual removal thereof is necessary, which presents a drawback in terms of productivity.